Nitrofurantoin redox biotransformation 135
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when it was added to microsomes before reducing agents.
This condition maintains the heme iron in its oxidized
state (Fe3ϩ), necessary requirement for the binding of
substrates to the enzyme. Thus, these results seem to
indicate that specific binding to the monooxygenase
occurs. Furthermore, this drug behaved as an inhibitor of
p-nitroanisole O-demethylation and naphthalene hydroxy-
lation. Changes on the “apparent kinetic” for naphthalene
hydroxylation elicited by nitrofurantoin are also in agree-
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It should be noted that CYP450 monooxygenases are
not specific enzymes, although the extent of the affinity
for lipophilic substrates widely differ. Therefore, using
liver preparations enriched in endoplasmic reticulum
(microsomes) to test CYP450 system activity (including
all the isoforms of CYP450 monooxygenases), compared
with reconstituted systems using purified enzymes seems
to be closer to what would occur in vivo. Altogether, our
results suggest that 1) inhibition of NADPH-elicited
microsomal lipid peroxidation by nitrofurantoin is likely
the consequence of its biotransformation through the
CYP450 oxidative system, and 2) nitrofurantoin is a likely
substrate of the CYP450 oxidative system. In agreement
with this hypothesis, hydroxylation metabolites of nitro-
furantoin have been identified [52,53]. In addition, 1-
aminohydantoin has been identified as a nitrofurantoin
metabolite in meat and milk products from animals treated
with nitrofurantoin [41,42]. Here, we show that 1-amin-
ohydantoin is specifically produced in vitro when rat liver
microsomes are incubated with nitrofurantoin under con-
ditions that allow its oxidative biotransformation through
the CYP450 system. These data strongly suggest that
nitrofurantoin can undergo oxidative biotransformation in
liver tissue. In light of these findings; several issues need
to be addressed to clearly understand oxidative stress asso-
ciated to the metabolism of nitrofurantoin in humans.
These include the actual contribution of the CYP450
reductase to oxidative stress arising from nitrofurantoin
nitro reduction. We are actively evaluating these issues.
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Declaration of interest
[19] Letelier ME, Izquierdo P, Godoy L, Lepe AM, Faúndez M.
Liver microsomal biotransformation of nitro-aryl drugs:
mechanism for potential oxidative stress induction. J Appl
Toxicol 2004;24:519–525.
The authors report no declarations of interest. The authors
alone are responsible for the content and writing of the
paper.
[20] Letelier ME, Entrala P, López-Alarcón C, González-Lira V,
Molina-Berríos A, Cortés-Troncoso J, et al. Nitroaryl-1,4-
dihydropyridines as antioxidants against rat liver microsomes
oxidation induced by iron/ascorbate, nitrofurantoin and naph-
thalene. Toxicol In Vitro 2007;21:1610–1618.
This work was funded by Laboratorios Ximena Polanco
(Santiago-Chile) and the FONDECYT [Grant #11090150].
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